Project Summary The goal of this project is to understand how interactions between host physiology, microbial metabolism and gut ecology interact to determine gut microbiome dynamics and gut homeostasis in the context of dietary variation. Gut microbes play key roles in the digestion of food, acquisition of nutrients, and defense against pathogens. The gut microbiota of omnivores must be able to maintain homeostasis and continue to carry out these functions in the face of a diverse and variable host diet. We propose to develop omnivorous cockroaches as a new model system for identifying and characterizing host and microbial responses to dietary shifts. Cockroaches are unusual among insects in that they host a highly diverse hindgut microbiota that is taxonomically and functionally analogous to the colonic microflora of humans. This property, along with their tractability to experimental and dietary manipulation, makes them ideal as a low-cost insect model for the study of gut microbiome homeostasis and dysbiosis. We have discovered that the gut microbiota of cockroaches is highly stable, with low individual-to-individual variability and exhibiting minimal variation in taxonomic profile in the face of major alterations in dietary composition. We hypothesize that this stability may be due to 1) host-microbe metabolic cross-feeding 2) stabilizing interactions and metabolic co-dependencies among gut microbes or 3) a high degree of metabolic flexibility in cockroach gut microbes. These hypotheses are not mutually exclusive, and multiple mechanisms may be acting in concert. We will test these hypotheses using a combination of molecular and experimental approaches. We will utilize metagenomic and metatranscriptomic techniques to study cockroach gut transcriptional and metabolic networks and how they change in response to dietary variation. We will also develop a culture library of abundant and ecologically important cockroach gut microbes to study gut microbial metabolic capabilities, genome variation, and nutritional dependencies. Follow- up studies will utilize gnotobiotic insects to study host-microbe and microbe-microbe interactions in simplified model communities, and will incorporate behavioral interventions to evaluate the role of environmental transmission and social behavior in shaping gut microbiome dynamics. Together, these efforts will extend our understanding of host and microbial contributions to gut homeostasis, and will enable the development of new and improved strategies to alter gut microbiome structure and function in humans.